In recent years, energy saving for an electrophotographic image forming apparatus has been demanded, and studies on so-called low temperature fixing by which fixing is conducted at lower temperature than in the past have been done in order to reduce energy consumption of a fixing device consuming the largest electric power in the image forming apparatus. As a technique to achieve the low temperature fixing, for example, a toner containing a binder resin exhibiting a low softening point and a low glass transition point temperature has been studied so as to smoothly conduct toner fusion even at low fixing temperature.
However, there appears a problem such that in the case of the toner with one exhibiting such a low softening point and such a low glass transition point temperature, toner-to-toner coagulation is easy to be generated by heat at high temperature during storage, and thither, there is another problem such that so-called tacking, by which image supports are attached to each other when fixed images having been formed with the toner are piled, is easy to be generated.
It is known that a toner particle constituting the toner can be designed to be one having a core/shell structure in which the surface of a toner mother particle is covered with a resin exhibiting high glass transition point temperature to improve toner-to-toner coagulation during storage.
On the other hand, in the situation where generation of tacking is dependent upon properties of a binder resin constituting a toner particle, that is, high or low glass transition point temperature of the binder resin, generation of tacking and achievement of low temperature fixing thereof are in the trade-off relationship, and the problem caused by this trade-off relationship has not yet been solved.